Ok, first, go to the AnimationSystem files for that weapon. These would be located at objects_server/weapons/handheld/(thegunyouaremodding)/AnimationSystem1p.inc.
Open it up with Notepad, and at the top of the document, there's a list of the animations with a time value you can edit. This is the time it takes to play that animation. Change the value to what you want, or if there isn't a time value under that animation, just add the line animationManager.length # and change it to the value you want.
You must also edit any necessary sounds so they play at the same speed as the animation.
If you're editing a reload, make sure to change the line ObjectTemplate.ammo.reloadTime to your new reload time.
(in the .tweak file of that weapon).
PM me if you somehow have problems.